Everybody now knows that there are big flat walls on the edge of newly generated areas in an old world from before 1.7.4 because of the new world generator, but tall, LONG, flat walls will appear WELL INSIDE the new areas. In the picture below, there is clearly a problem in the world generator, and I know it, causing several mis-developed areas. There are many more walls like this throughout the new area. Because this bug is apparent, it would be fantastic if Mojang could look into this.

-Diavel222